Formed sheet of thermalconductive silicone gel and method for producing the same

ABSTRACT

A formed sheet of thermalconductive silicone gel is provided. The formed sheet has (i) a thin film reinforcement layer hardened into rubber only in a surface layer on the upper side, the lower side, or both sides, (ii) a sheet-shaped reinforcement material buried in a surface layer of the upper or the lower side, or (iii) a sheet-shaped reinforcement material buried in a surface layer of the upper side or the lower side of the sheet, and a thin film reinforcement layer hardened into rubber in this surface layer or in a surface layer on both sides of the sheet. The formed sheet of thermalconductive silicone gel has low compressibility, high strength, is easy to handle during the mounting process, and can be reused after its contact compression between a chip and a heat sink has been released.

This application is a Divisional of application Ser. No. 08/961,535,filed Oct. 30, 1997, now U.S. Pat. No. 6,083,853 which application(s)are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a thermalconductive sheet that is usedas a member of a heat dissipation and cooling structure for heatgenerating electronic parts and the like, especially to athermalconductive sheet with low rigidity that is used for dissipatingheat and cooling of heat generating electronic parts and the like.

BACKGROUND OF THE INVENTION

In the past, the following types of thermalconductive sheets with lowrigidity have been proposed as a member of a heat dissipation andcooling structure for heat generating electronic parts and the like:

(1) A thermalconductive sheet that is not deformed or damaged by thecompression of a heat generating electronic member (referred to below as"chip") and a heat sink, because the compression load on the sheet isheld low when the sheet is compressed to establish a tight contact(referred to below as "contact compression") between the chip and theheat sink.

(2) A thermalconductive sheet that is tightly contacted when beingcontact-compressed between a chip and a heat sink having an unevensurface on the contact side, because the thermalconductive sheet iselastic, thus ensuring a sufficiently large thermalconductive surface.

(3) A thermalconductive sheet that (a) has sufficiently tight contactwith all of a plurality of chips mounted on a board, and (b) that is notdeformed or damaged by the compression of the chips and a heat sink whenbeing contact-compressed between the plurality of chips and the heatsink, because the thermalconductive sheet is elastic.

A silicone gel sheet containing a thermalconductive filler, and JapaneseTokkai No. Hei 2-166755, No. Hei 2-196453, and No. Hei 6-155517 areknown as examples for such thermalconductive sheets.

However, a silicone gel sheet containing a thermalconductive filler, anda thermalconductive silicone gel sheet having grooves on one or bothsides (Tokkai Hei 2-166755), are extremely soft and lack strength, andtherefore pose severe problems regarding the handling of the sheetsduring the mounting process. Furthermore, because both sides of thesheet have roughly the same degree of stickiness, the sheet may stick toboth the chip and the heat sink when releasing the contact compressionbetween the chip and the heat sink for maintenance after the mounting,resulting in extreme deformation or even rupture, and thus making reuseof the sheet impossible.

A compound thermalconductive sheet, wherein a silicone gel containing athermalconductive filler is layered and hardened on a silicone rubbersheet containing a thermalconductive filler (Tokkai Hei 2-196453), and athermalconductive compound sheet, wherein a low rigidity silicone rubbercontaining a thermalconductive filler is integrated with a sheet made bycoating a meshed reinforcement material with a silicone rubbercontaining a thermalconductive filler and then hardened (Tokkai Hei2-196453), are both soft in a direction perpendicular to the sheet,rigid in the in-plane direction and sticky only on one side andtherefore easy to handle during the mounting process and can be reusedafter release of the contact compression. However, because thecompressibility of such sheets is about 2 to 5 times higher than thecompressibility of a single thermalconductive silicone gel sheet, thesesheets cannot be used when the mounting electronic parts such as chips,heat sinks, and boards having low rigidity, or when the heightdifference of a plurality of chips mounted on a board is large.

SUMMARY OF THE INVENTION

It is the purpose of the present invention to overcome the problems ofthe prior art by providing a formed sheet of thermalconductive siliconegel that has a low compressibility and a high rigidity, that is easy tohandle during the mounting process, and that can be reused after therelease of the contact compression with a chip and a heat sink.

A first formed sheet of thermalconductive silicone gel according to thepresent invention is characterized in that a thin film reinforcementlayer is hardened into rubber in a surface layer on at least one side ofthe sheet.

In the first formed sheet of thermalconductive silicone gel according tothe present invention it is preferable that a silicone gel containing athermalconductive filler is sandwiched between (a) a resin film to whichhas been applied an organohydrogen polysiloxane containing at least twohydrogen atoms bonded to a silicon atom in each molecule and (b) a resinfilm to which said organohydrogen polysiloxane has not been applied, orsandwiched between two resin films to which said organohydrogenpolysiloxane has been applied; rolled by being continually passedthrough at least one pair of rolls; continually passed through a heatingfurnace; and hardened; in order to form a thin film reinforcement layerhardened into rubber on at least one side of the sheet.

A second formed sheet of thermalconductive silicone gel according to thepresent invention is characterized in that a thin film reinforcementlayer is hardened into rubber in a surface layer on at least one side ofthe sheet, and a sheet-shaped reinforcement material is buried in asurface layer on one side of the sheet.

In the second formed sheet of thermalconductive silicone gel accordingto the present invention, it is preferable that a silicone gelcontaining a thermalconductive filler is sandwiched between (a) a resinfilm having a surface to which has been applied an organohydrogenpolysiloxane containing at least two hydrogen atoms bonded to a siliconatom in each molecule, and onto which surface a sheet-shapedreinforcement layer has been layered and (b) a resin film to which saidorganohydrogen polysiloxane has not been applied, or between two resinfilms to which said organohydrogen polysiloxane has been applied; rolledby being continually passed through at least one pair of rolls;continually passed through a heating furnace; and hardened; in order toform a sheet-shaped reinforcement material buried in a surface layer onone side of the sheet and a thin film reinforcement layer hardened intorubber on at least one side of the sheet.

In the first and second formed sheet of thermalconductive silicone gelaccording to the present invention, it is preferable that the hardnessof the thin film reinforcement layer is in the range of 10-95 whenmeasured with an ASKER F hardness meter. It is even more preferable thatthe hardness of the thin film reinforcement layer is in the range of20-70 when measured with an ASKER F hardness meter.

In the first and second formed sheet of thermalconductive silicone gelaccording to the present invention, it is preferable that the thicknessof the thin film reinforcement layer is in the range of 0.01-0.5 mm. Itis even more preferable that the thickness of the thin filmreinforcement layer is in the range of 0.01-0.1 mm.

A third formed sheet of thermalconductive silicone gel according to thepresent invention is characterized in that a sheet-shaped reinforcementmaterial is buried in a surface layer on one side of a formed sheet ofsilicon gel containing a thermalconductive filler.

In the third formed sheet of thermalconductive silicone gel according tothe present invention, it is preferable that a silicone gel containing athermalconductive filler is sandwiched between (a) a resin film ontowhose surface a sheet-shaped reinforcement layer has been layered and(b) a resin film onto whose surface a sheet-shaped reinforcement layerhas not been layered; rolled by being continually passed through atleast one pair of rolls; continually passed through a heating furnace;and hardened; in order to form to form a sheet-shaped reinforcementmaterial buried in a surface layer on one side of the sheet.

In the second and third formed sheet of thermalconductive silicone gelaccording to the present invention, it is preferable that the depth towhich the sheet-shaped reinforcement material is buried in a surfacelayer on one side of the sheet is in the range of more than 0 mm but notmore than 1 mm. Here, the term "depth" indicates the distance from theupper surface of the reinforcement material to the upper surface of thegel. It is even more preferable that the depth to which the sheet-shapedreinforcement material is buried in a surface layer on one side of thesheet is in the range of more than 0 mm but not more than 0.5 mm.

In the second and third formed sheet of thermalconductive silicone gelaccording to the present invention, it is preferable that thesheet-shaped reinforcement material buried in a surface layer on oneside of the sheet has a mesh fabric structure using at least one fiberselected from synthetic fiber and natural fiber.

A first method of manufacturing a formed sheet of thermalconductivesilicone gel according to the present invention comprises the steps of:sandwiching a silicone gel containing a thermalconductive filler between(a) a resin film to which has been applied an organohydrogenpolysiloxane containing at least two hydrogen atoms bonded to a siliconatom in each molecule and (b) a resin film to which said organohydrogenpolysiloxane has not been applied, or sandwiching said silicone gelbetween two resin films to which said organohydrogen polysiloxane hasbeen applied; rolling the silicone gel by continually passing thesilicone gel through at least one pair of rolls; and hardening thesilicone gel by continually passing the silicone gel through a heatingfurnace.

A second method of manufacturing a formed sheet of thermalconductivesilicone gel according to the present invention comprises the steps of:sandwiching a silicone gel containing a thermalconductive filler between(a) a resin film having a surface to which has been applied anorganohydrogen polysiloxane containing at least two hydrogen atomsbonded to a silicon atom in each molecule, and onto which surface asheet-shaped reinforcement layer has been layered and (b) a resin filmto which said organohydrogen polysiloxane has not been applied, orsandwiching the silicone gel between two resin films to which saidorganohydrogen polysiloxane has been applied; rolling the silicone gelby being continually passing it through at least one pair of rolls; andhardening the silicone gel by continually passing the silicone gelthrough a heating furnace.

A third method of manufacturing a formed sheet of thermalconductivesilicone gel according to the present invention comprises the steps of:sandwiching a silicone gel containing a thermalconductive filler between(a) a resin film onto whose surface a sheet-shaped reinforcement layerhas been layered and (b) a resin film onto whose surface a sheet-shapedreinforcement layer has not been layered; rolling the silicone gel bybeing continually passed through at least one pair of rolls; andhardening the silicone gel by continually passing the silicone gelthrough a heating furnace.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 A and B are a sectional views of a formed sheet ofthermalconductive silicone gel according to a first example of thepresent invention.

FIG. 2 is a sectional view of a formed sheet of thermalconductivesilicone gel according to a second example of the present invention.

FIGS. 3 A and B are sectional views of a formed sheet ofthermalconductive silicone gel according to a third example of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

To obtain a formed sheet of thermalconductive silicone gel, one of thefollowing five procedures can be used when forming the silicone gelcontaining a thermalconductive filler. The resulting formed sheet ofthermalconductive silicone gel has low compressibility, high strength,is easy to handle during the mounting process, and can be reused afterthe contact compression between the chip and the heat sink has beenreleased.

Procedure 1

The not yet hardened silicone gel containing a thermalconductive filleris placed onto a resin film, and an organohydrogen polysiloxanecontaining at least two hydrogen atoms bonded to a silicon atom in eachmolecule is applied from above the silicone gel to its surface.

Another resin film is placed on top of the silicone gel, which is thenshaped into sheet form and hardened between the two resin films. Theresult is a formed sheet of thermalconductive silicone gel having a thinfilm reinforcement layer hardened into rubber only in a surface layer towhich the organohydrogen polysiloxane was applied. Preferable formationmethods for this procedure are press forming, coating forming andcalender forming.

In addition, a formed sheet of thermalconductive silicone gel having athin film reinforcement layer hardened into rubber only in said surfacelayer was produced by the following method using roll forming: Asilicone gel containing a thermalconductive filler was sandwichedbetween (a) a resin film to which has been applied an organohydrogenpolysiloxane containing at least two hydrogen atoms bonded to a siliconatom in each molecule and (b) a resin film to which said organohydrogenpolysiloxane has not been applied, and was then rolled by beingcontinually passed through at least one pair of rolls.

When the rolled sheet is continually passed through a heating furnaceand hardened, then the silicone gel containing a thermalconductivefiller becomes a formed sheet of thermalconductive silicone gel having athin film reinforcement layer hardened into rubber only in the surfacelayer to which said organohydrogen polysiloxane has been applied.

Procedure 2

A silicone gel containing a thermalconductive filler is placed betweentwo resin films, to whose surface an organohydrogen polysiloxanecontaining at least two hydrogen atoms bonded to a silicon atom in eachmolecule has been applied. The silicone gel is then shaped into sheetform and hardened.

The result is a formed sheet of thermalconductive silicone gel having athin film reinforcement layer hardened into rubber only in a surfacelayer on the upper and lower sides of the sheet. Preferable formationmethods for this procedure are press forming, coating forming andcalender forming.

Furthermore, a formed sheet of thermalconductive silicone gel having athin film reinforcement layer hardened into rubber only in said surfacelayer was produced by the following method using roll forming: Asilicone gel containing a thermalconductive filler was sandwichedbetween two resin films to which has been applied an organohydrogenpolysiloxane containing at least two hydrogen atoms bonded to a siliconatom in each molecule, and was then rolled by being passed through atleast one pair of rolls.

When the rolled sheet is continually passed through a heating furnaceand hardened, then the silicone gel containing a thermalconductivefiller becomes a formed sheet of thermalconductive silicone gel having athin film reinforcement layer hardened into rubber only on the upper andlower surface layers.

Procedure 3

A not yet hardened silicone gel containing a thermalconductive filler isplaced onto a resin film, a sheet-shaped reinforcement material andanother resin film are placed on top of the silicone gel, and thesilicone gel is shaped into sheet form and hardened. The silicone gelcontaining a thermalconductive filler, which silicone gel is hardenedbetween the two resin films becomes a formed sheet of thermalconductivesilicone gel having a sheet-formed reinforcement material buried in onesurface layer of the hardened sheet. Preferable formation methods forthis procedure are press forming, coating forming and calender forming.

Furthermore, a formed sheet of thermalconductive silicone gel having asheet-formed reinforcement material buried in one surface layer of thehardened sheet was produced by the following method using roll forming:A silicone gel containing a thermalconductive filler was sandwichedbetween a resin film onto whose surface a sheet-shaped reinforcementlayer has been layered and a resin film onto whose surface asheet-shaped reinforcement layer has not been layered, and was thenrolled by being passed through at least one pair of rolls.

When the rolled sheet is continually passed through a heating furnaceand hardened, then the silicone gel containing a thermalconductivefiller becomes a formed sheet of thermalconductive silicone gel having asheet-shaped reinforcement material buried in a surface layer on oneside of the hardened sheet.

Procedure 4

A formed sheet of thermalconductive silicone gel having a sheet-shapedreinforcement material buried in a surface layer on one side of thehardened sheet, and a thin film reinforcement layer hardened into rubberonly in a surface layer of the same side was produced by combiningprocedures 1 and 3. Applicable formation methods for this procedure arepress forming, coating forming and calender forming, but methods basedon roll forming can be used as well.

Procedure 5

A formed sheet of thermalconductive silicone gel having a sheet-shapedreinforcement material buried in a surface layer on one side of thehardened sheet, and a thin film reinforcement layer hardened into rubberonly in a surface layer of both sides of the sheet was produced bycombining procedures 2 and 3. Applicable formation methods for thisprocedure are press forming, coating forming and calender forming, butmethods based on roll forming can be used as well. A formed sheet ofthermalconductive silicone gel according to the present invention,produced with one of the above methods, provides the followingadvantages:

Advantage 1

The formed sheet of thermalconductive silicone gel having a thin filmreinforcement layer hardened into rubber in a surface layer on the upperside, the lower side or on both sides is not prone to extremedeformation or rupture during the mounting process, and thus is easierto handle. Not only can the orientation of the sheet be chosen at thetime of its adhesion, but also the formed sheet of thermalconductivesilicone gel is not sticky on both sides, because the stickiness of thesurface of the thin film reinforcement layer becomes negligible when itis hardened into rubber. Thus, when the contact compression of the chipand the heat sink is released for maintenance after the mounting, thesheet is not easily stretched apart so that it deforms extremely orbreaks. Furthermore, when all portions of the sheet other than thehardened thin film reinforcement layer are extremely soft, the samecharacteristics of flexibility and compressibility in a directionperpendicular to the sheet as in a thermalconductive silicone gel sheethaving no thin film reinforcement layer can be obtained.

Advantage 2

When a sheet-shaped reinforcement material is buried in a surface layerof the upper or the lower side, the strength of the thermalconductivesilicone gel sheet is increased, and the sheet is easier to handleduring the mounting process and is not easily ruptured during thecontact compression due to extreme unevenness of the contact compressionsurface of the chip or the heat sink. Furthermore, when the sheet-shapedreinforcement material is buried in a surface layer on one side, thecompressibility can be suppressed to a lower value as compared to whenthe sheet-shaped reinforcement material is buried in a location otherthan a surface layer.

Advantage 3

When a sheet-shaped reinforcement material is buried in a surface layeron the upper or the lower side of the sheet, and the sheet has a thinfilm reinforcement layer hardened into rubber in this surface layer orin a surface layer on both sides, then the sheet can be handled evenmore easily than previously described under Advantage 2, because thestickiness of the thin film reinforcement layer hardened into rubberbecomes negligible.

EXAMPLES

In the following, the present invention is explained in detail withreference to the drawings.

Example 1

FIGS. 1 A and B are sectional drawings showing a first example of afirst formed sheet of thermalconductive silicone gel according to thepresent invention. As is shown in FIGS. 1 A and B, this formed sheet ofthermalconductive silicone gel is composed of a silicone gel layer 1containing a thermalconductive filler, and a thin film reinforcementlayer 2, wherein a silicone gel containing a thermalconductive fillerwas hardened into rubber. FIG. 1 A shows an example wherein the thinfilm reinforcement layer 2 is formed only in a surface layer on one sideof the silicone gel layer 1 containing a thermalconductive filler,whereas FIG. 1 B shows an example wherein the thin film reinforcementlayer 2 is formed in a surface layer on both sides of the silicone gellayer 1 containing a thermalconductive filler.

For the silicone gel layer 1 and the thin film reinforcement layer 2, asilicone gel, containing the same thermalconductive filler, hardened byan addition reaction is used. In addition, at the hardening andformation time, the silicone gel is sandwiched between a polyester (PET)film to which about 5 μm of an organohydrogen polysiloxane containing atleast two hydrogen atoms bonded to a silicon atom in each molecule havebeen applied, and a PET film to which said organohydrogen polysiloxanehas not been applied. Alternatively, the silicone gel is sandwichedbetween two PET films to which said organohydrogen polysiloxane has beenapplied. After the silicone gel is rolled by being passed through a pairof rolls, it is continually passed through a heating furnace. Thus, athin film reinforcement layer hardened into rubber can be formed in asurface layer of one side or both sides of the sheet. The PET film isremoved from the silicone gel after the hardening.

The silicone gel layer 1, containing a thermalconductive filler, and thethin film reinforcement layer 2, which has been hardened into rubber,can be produced by using one of the following silicone gels containing athermalconductive filler hardened by an addition reaction,.

(1) Silicone Gel Composition, Containing a Thermalconductive filler

Sarcon GR A/B (Hardness Asker F 57): Product of Fuji Polymer Ind., Co.

Sarcon GR-a A/B (Hardness Asker F 54): Product of Fuji Polymer Ind., Co.

SE4445CV A/B (Hardness Asker F 47): Product of Dow Corning ToraySilicone Co.

(2) Organohydrogen Polysiloxane Containing at least Two Hydrogen AtomsBonded to a Silicon Atom in each Molecule

SH-1107: Product of Dow Corning Toray Silicone, Co.

RD-1: Product of Dow Corning Toray Silicone, Co.

Using the above compositions, the silicone gel is sandwiched between tworesin films. After the silicone gel is rolled by being passed through apair of rolls, it is passed through a heating furnace with an internalfurnace temperature of 280° C. and a passage velocity through thefurnace of 3 m/min. The characteristics of the formed sheet ofthermalconductive silicone gel obtained under these conditions are shownin Table 1 and 2. The figures shown in these tables refer to a samplehaving a 1.0 mm thick silicone gel layer 1 and a 0.03 mm thick thin filmreinforcement layer 2, and to a sample with a 2.0 mm thick silicone gellayer 1 and a 0.05 mm thick thin film reinforcement layer 2. Thecomparative sample has, except for the differences pointed out in theremarks to the table, the same composition as the example. This is alsotrue for all following examples.

                  TABLE 1                                                         ______________________________________                                        Typical product properties of Example 1, using Sarcon GR - a A/B              Sample A        Comp. Sample                                                                              Testing Method                                    ______________________________________                                        Thermal 1.5         1.5         Unsteady Hot Wire                             Conductivity                                                                                                  Method                                        (W/m · K)                                                            Thermal                                                                       Resistance                                                                    (° C./W)                                                               1.0 mm  0.78        0.78        Transistor: TO-3                              2.0 mm  1.50        1.50        Appl. Power: 20 W                                                             for 5 min                                                                     Load: 2 kgf                                   Compression                                                                   Load (kgf)                                                                    Compres-                                                                              1.0 mm  2.0 mm  1.0 mm                                                                              2.0 mm                                                                              Sample Size:                              sion Rate                           25 mm × 25 mm                       10%     21.5    11.9    16.2  8.0   Compression. Vel.:                        20%     46.5    20.5    35.9  15.9  5 mm/min                                  30%     72.1    31.5    49.7  22.9  Load Cell:                                40%     104.4   47.4    64.5  33.1  200 kgf                                   ______________________________________                                         Remarks: Sample A is composed of a formed sheet of thermalconductive          silicone gel with a thin film reinforcement layer formed in a surface         layer of one side of the sheet. The Comparative Sample is composed of a       formed sheet of thermalconductive silicone gel without the thin film          reinforcement layer.                                                     

                  TABLE 2                                                         ______________________________________                                        Typical material properties of Example 1, using Sarcon GR - a A/B                               Comp.                                                                  Sample A                                                                             Sample   Testing Method                                     ______________________________________                                        Color        gray-black                                                                             gray-black                                                                             --                                             Spec. Gravity                                                                              2.4      2.4      Water Displacement                                                            Method                                         Tens. Strength (kgf/cm.sup.2)                                                              4        3        JIS-K-6301 (No. 2)                             Extensibility (%)                                                                          270      340      JIS-K-6301 (No. 2)                             Tear. Strength (kgf/cm)                                                                    3        2        JIS-K-6301 (Type B)                            Vol. Resistivity (Ω · cm)                                                   1 × 10.sup.13                                                                    1 × 10.sup.13                                                                    JIS-C-2123                                     Isolation Breakdown                                                                        18       18       JIS-C-2123                                     Voltage (kV/mm)                                                               Withstand Voltage                                                                          14       14       JIS-C-2123                                     (kV/mm)                                                                       ______________________________________                                         Remarks: Sample A is composed of a formed sheet of thermalconductive          silicone gel with a thin film reinforcement layer formed in a surface         layer of one side of the sheet. The Comparative Sample is composed of a       formed sheet of thermalconductive silicone gel without the thin film          reinforcement layer.                                                     

As becomes clear from Tables 1 and 2, the thermal resistance of thepresent example (Sample A) is low, the compressibility is keptcomparatively low, the tensile strength and the tearing strength arehigh, the extensibility is low, and the handling properties during themounting process are good. Reuse of the formed sheet ofthermalconductive silicone gel after the compression release of the chipand the heat sink was possible.

Example 2

Next, a second example of a first formed sheet of thermalconductivesilicone gel according to the present invention is explained. The formedsheet of thermalconductive silicone gel of this example is shown inFIGS. 1 A and B.

In the present example, for the silicone gel layer 1 and the thin filmreinforcement layer 2, a silicone gel containing the samethermalconductive filler is used. In addition, at the hardening andformation time, the silicone gel is covered on one side with apolypropylene (PP) film to which about 5 μm of an organohydrogenpolysiloxane containing at least two hydrogen atoms bonded to a siliconatom in each molecule have been applied, and on the other side with a PPfilm to which said organohydrogen polysiloxane has not been applied.Alternatively, the silicone gel is covered on both sides with PP filmsto which said organohydrogen polysiloxane has been applied. Thus, a thinfilm reinforcement layer hardened into rubber can be formed in a surfacelayer of one side or both sides of the sheet.

The silicone gel layer 1, containing a thermalconductive filler, and thethin film reinforcement layer 2, which has been hardened into rubber,can be produced by using one of the following addition reaction typethermalconductive silicone composition.

(1) Silicone Gel Composition, Containing a Thermalconductive filler

Sarcon GR A/B (Hardness Asker F 57): Product of Fuji Polymer Ind., Co.

Sarcon GR-a A/B (Hardness Asker F 54): Product of Fuji Polymer Ind., Co.

SE4445CV A/B (Hardness Asker F 47): Product of Dow Corning ToraySilicone Co.

(2) Organohydrogen Polysiloxane Containing at least Two Hydrogen AtomsBonded to a Silicon Atom in each Molecule

SH-1107: Product of Dow Corning Toray Silicone, Co.

RD-1: Product of Dow Corning Toray Silicone, Co.

Using the above compositions, the silicone gel is formed by the pressforming method. The characteristics of a formed sheet ofthermalconductive silicone gel obtained at 100° C. forming temperature,3 min forming time, and 100 kgf/cm² forming pressure are shown in Table3 and 4. The figures shown in these tables refer to a sample having a1.0 mm thick silicone gel layer 1 and a 0.03 mm thick thin filmreinforcement layer 2, and to a sample with a 2.0 mm thick silicone gellayer 1 and a 0.05 mm thick thin film reinforcement layer 2.

                  TABLE 3                                                         ______________________________________                                        Typical product properties of Example 2, using Sarcon GR - a A/B              Sample B        Comp. Sample                                                                              Testing Method                                    ______________________________________                                        Thermal 1.5         1.5         Unsteady Hot Wire                             Conductivity                    Method                                        (W/m · K)                                                            Thermal                                                                       Resistance                                                                    (° C./W)                                                               1.0 mm  1.01        0.78        Transistor: TO-3                              2.0 mm  1.52        1.45        Appl. Power: 20 W                                                             for 5 min                                                                     Load: 2 kgf                                   Compression                                                                   Load (kgf)                                                                    Compres-                                                                              1.0 mm  2.0 mm  1.0 mm                                                                              2.0 mm                                                                              Sample Size:                              sion Rate                           25 mm × 25 mm                       10%     25.5    22.2    18.5  13.2  Compression. Vel.:                        20%     57.3    40.2    41.8  23.1  5 mm/min                                  30%     83.5    62.5    58.9  34.8  Load Cell:                                40%     115.9   92.3    80.4  51.6  200 kgf                                   ______________________________________                                         Remarks: Sample B is composed of a formed sheet of thermalconductive          silicone gel with a thin film reinforcement layer formed in a surface         layer of one side of the sheet. The Comparative Sample is composed of a       formed sheet of thermalconductive silicone gel without the thin film          reinforcement layer.                                                     

                  TABLE 4                                                         ______________________________________                                        Typical material properties of Example 2 using Sarcon GR - a A/B                                Comp.                                                                  Sample B                                                                             Sample   Testing Method                                     ______________________________________                                        Color        gray-black                                                                             gray-black                                                                             --                                             Spec. Gravity                                                                              2.4      2.4      Water Displacement                                                            Method                                         Tens. Strength (kgf/cm.sup.2)                                                              4        3        JIS-K-6301 (No. 2)                             Extensibility (%)                                                                          270      340      JIS-K-6301 (No. 2)                             Tear. Strength (kgf/cm)                                                                    3        2        JIS-K-6301 (Type B)                            Vol. Resistivity (Ω · cm)                                                   1 × 10.sup.13                                                                    1 × 10.sup.13                                                                    JIS-C-2123                                     Isolation Breakdown                                                                        18       18       JIS-C-2123                                     Voltage (kV/mm)                                                               Withstand Voltage                                                                          14       14       JIS-C-2123                                     (kV/mm)                                                                       ______________________________________                                         Remarks: Sample B is composed of a formed sheet of thermalconductive          silicone gel with a thin film reinforcement layer formed in a surface         layer of one side of the sheet. The Comparative Sample is composed of a       formed sheet of thermalconductive silicone gel without the thin film          reinforcement layer.                                                     

As becomes clear from Tables 3 and 4, the thermal resistance of thepresent example (Sample B) is low, the compressibility is low, thetensile strength and the tearing strength are high, the extensibility islow, and the handling properties during the mounting process are good.Reuse of the formed sheet of thermalconductive silicone gel after thecompression release of the chip and the heat sink was possible.

Example 3

FIG. 2 is a sectional drawing showing a first example of a second formedsheet of thermalconductive silicone gel according to the presentinvention. As is shown in FIG. 2, this formed sheet of thermalconductivesilicone gel is composed of a silicone gel layer 1 containing athermalconductive filler, and a sheet-shaped reinforcement material 3.FIG. 2 shows an example wherein the reinforcement material 3 is buriedin a surface layer on one side of the silicone gel layer 1 containing athermalconductive filler, thereby completely covering the reinforcementmaterial.

A mesh fabric of polyester fiber, heat-proof nylon fiber, aramid fiber,cotton fiber or the like can be used for the sheet-shaped reinforcementmaterial 3. However, considering the thermal tolerance, polyester fiberor heat-proof nylon fiber is preferable.

The silicone gel layer 1 containing a thermalconductive filler and thesheet-shaped reinforcement material 3 can be produced by using one ofthe compositions below.

(1) Silicone Gel Composition, Containing a Thermalconductive filler

Sarcon GR A/B (Hardness Asker F 57): Product of Fuji Polymer Ind., Co.

Sarcon GR-a A/B (Hardness Asker F 54): Product of Fuji Polymer Ind., Co.

SE4445CV A/B (Hardness Asker F 47): Product of Dow Corning ToraySilicone Co.

(2) Sheet-Shaped Reinforcement Material (Mesh fabric of Nylon Fiber)

Nylon-ture N-5035

Using the above compositions, the silicone gel is sandwiched betweenresin films. After the silicone gel is rolled by being passed through apair of rolls, it is passed through a heating furnace with an internalfurnace temperature of 280° C. and a passage velocity through thefurnace of 3 m/min. The characteristics of the formed sheet ofthermalconductive silicone gel obtained under these conditions are shownin Table 5 and 6. The figures shown in these tables refer to a samplehaving a 1.0 mm thick silicone gel layer 1 and a reinforcement material3 buried to a depth of about 0.2 mm in the silicone gel layer 1, and toa sample with a 2.0 mm thick silicone gel layer 1 and a reinforcementmaterial 3 buried to a depth of about 0.3 mm in the silicone gellayer 1. The term "depth" indicates the distance from the upper surfaceof the reinforcement material to the upper surface of the gel.

                  TABLE 5                                                         ______________________________________                                        Typical product properties of Example 3, using Sarcon GR - a A/B              Sample C        Comp. Sample                                                                              Testing Method                                    ______________________________________                                        Thermal 1.5         1.5         Unsteady Hot Wire                             Conductivity                     Method                                       (W/m · K)                                                            Thermal                                                                       Resistance                                                                    (° C./W)                                                               1.0 mm  0.80        0.80        Transistor: TO-3                              2.0 mm  1.50        1.50        Allp. Power: 20 W                                                             for 5 min                                                                     Load: 2 kgf                                   Compression                                                                   Load (kgf)                                                                    Compres-                                                                              1.0 mm  2.0 mm  1.0 mm                                                                              2.0 mm                                                                              Sample Size:                              sion Rate                           25 mm × 25 mm                       10%     18.4    12.4    29.6  22.6  Compression. Vel.:                        20%     50.2    30.9    65.7  48.3  5 mm/min                                  30%     78.1    53.6    107.8 81.1  Load Cell:                                40%     108.8   82.1    154.5 118.1 200 kgf                                   ______________________________________                                         Remarks: Sample C is composed of a formed sheet of thermalconductive          silicone gel with a buried sheetshaped reinforcement material in a surfac     layer of one side of the sheet. The Comparative Sample is composed of a       formed sheet of thermalconductive silicone gel with a buried sheetshaped      reinforcement material in a center portion of the sheet.                 

                  TABLE 6                                                         ______________________________________                                        Typical material properties of Example 3, using Sarcon GR - a A/B                               Comp.                                                                  Sample C                                                                             Sample   Testing Method                                     ______________________________________                                        Color        gray-black                                                                             gray-black                                                                             --                                             Spec. Gravity                                                                              2.4      2.4      Water Displacement                                                            Method                                         Tens. Strength (kgf/cm.sup.2)                                                              5        5        JIS-K-6301 (No. 2)                             Extensibility (%)                                                                          100      100      JIS-K-6301 (No. 2)                             Tear. Strength (kgf/cm)                                                                    4        4        JIS-K-6301 (Type B)                            Vol. Resistivity (Ω · cm)                                                   1 × 10.sup.13                                                                    1 × 10.sup.13                                                                    JIS-C-2123                                     Isolation Breakdown                                                                        16       16       JIS-C-2123                                     Voltage (kV/mm)                                                               Withstand Voltage                                                                          13       13       JIS-C-2123                                     (kV/mm)                                                                       ______________________________________                                         Remarks: Sample C is composed of a formed sheet of thermalconductive          silicone gel with a buried sheetshaped reinforcement material in a surfac     layer of one side of the sheet. The Comparative Sample is composed of a       formed sheet of thermalconductive silicone gel with a buried sheetshaped      reinforcement material in a center portion of the sheet.                 

As becomes clear from Tables 5 and 6, the thermal resistance of thepresent example (Sample C) is low, the compressibility is low, thetensile strength and the tearing strength are high, the extensibility islow, and the handling properties during the mounting process are good.Reuse of the formed sheet of thermalconductive silicone gel after thecompression release of the chip and the heat sink was possible.

Example 4

Next, a second example of a second formed sheet of thermalconductivesilicone gel according to the present invention is explained. The formedsheet of thermalconductive silicone gel of this second example is shownin FIG. 2.

A mesh fabric of polyester fiber, heat-proof nylon fiber, aramid fiber,cotton fiber or the like can be used for the sheet-shaped reinforcementmaterial 3. However, considering the thermal tolerance, polyester fiberor heat-proof nylon fiber are preferable.

The silicone gel layer 1 containing a thermalconductive filler and thesheet-shaped reinforcement material 3 can be produced by using one thecompositions below.

(1) Silicone Gel Composition, Containing a Thermalconductive filler

Sarcon GR A/B (Hardness Asker F 57): Product of Fuji Polymer Ind., Co.

Sarcon GR-a A/B (Hardness Asker F 54): Product of Fuji Polymer Ind., Co.

SE4445CV A/B (Hardness Asker F 47): Product of Dow Corning ToraySilicone Co.

(2) Sheet-Shaped Reinforcement Material (Mesh fabric of Polyester Fiber)

Russell-Net T-280

Russell-Net T-180-50D

Using the above compositions, the silicone gel is formed by the pressforming method. The characteristics of a formed sheet ofthermalconductive silicone gel obtained at 100° C. forming temperature,3 min forming time, and 100 kgf/cm² forming pressure are shown in Table7 and 8. The figures shown in these tables refer to a sample having a1.0 mm thick silicone gel layer 1 and a reinforcement layer 3 with aweight per area of 55 g/m² (Russell-Net T-280) buried to a depth ofabout 0.2 mm in the silicone gel layer 1, and to a sample with a 2.0 mmthick silicone gel layer 1 and a reinforcement layer 3 with a weight perarea of 55 g/m² (Russell-Net T-280) buried to a depth of about 0.3 mm inthe silicone gel layer 1.

                  TABLE 7                                                         ______________________________________                                        Typical product properties of Example 4, using Sarcon GR - a A/B              Sample D        Comp. Sample                                                                              Testing Method                                    ______________________________________                                        Thermal 1.5         1.5         Unsteady Hot Wire                             Conductivity                    Method                                        (W/m · K)                                                            Thermal                                                                       Resistance                                                                    (° C./W)                                                               1.0 mm  1.03        0.78        Transistor: TO-3                              2.0 mm  1.72        1.45        Appl. Power: 20 W                                                             for 5 min                                                                     Load: 2 kgf                                   Compression                                                                   Load (kgf)                                                                    Compres-                                                                              1.0 mm  2.0 mm   1.0 mm                                                                             2.0 mm                                                                               Sample Size:                             sion Rate                           25 mm × 25 mm                       10%     22.4    20.6    55.5  39.6  Compression. Vel.:                        20%     63.0    50.7    125.4 69.3  5 mm/min                                  30%     108.7   88.2    176.7 104.4  Load Cell:                               40%     157.5   129.9   >200     154.8                                                                              200 kgf                                 ______________________________________                                         Remarks: Sample D is composed of a formed sheet of thermalconductive          silicone gel with a buried sheetshaped reinforcement material in a surfac     layer of one side of the sheet. The Comparative Sample is composed of a       formed sheet of thermalconductive silicone gel with a buried sheetshaped      reinforcement material in a center portion of the sheet.                 

                  TABLE 8                                                         ______________________________________                                        Typical material properties of Example 4, using Sarcon GR - a A/B                               Comp.                                                                  Sample D                                                                             Sample   Testing Method                                     ______________________________________                                        Color        gray-black                                                                             gray-black                                                                             --                                             Spec. Gravity                                                                              2.3      2.3      Water Displacement                                                            Method                                         Tens. Strength (kgf/cm.sup.2)                                                              18       18       JIS-K-6301 (No. 2)                             Extensibility (%)                                                                          180      180      JIS-K-6301 (No. 2)                             Tear. Strength (kgf/cm)                                                                    7        7        JIS-K-6301 (Type B)                            Vol. Resistivity (Ω · cm)                                                   1 × 10.sup.13                                                                    1 × 10.sup.13                                                                     JIS-C-2123                                    Isolation Breakdown                                                                        18       18       JIS-C-2123                                     Voltage (kV/mm)                                                               Withstand Voltage                                                                          14       14       JIS-C-2123                                     (kV/mm)                                                                       ______________________________________                                         Remarks: Sample D is composed of a formed sheet of thermalconductive          silicone gel with a buried sheetshaped reinforcement material in a surfac     layer of one side of the sheet. The Comparative Sample is composed of a       formed sheet of thermalconductive silicone gel with a buried sheetshaped      reinforcement material in a center portion of the sheet.                 

As becomes clear from Tables 7 and 8, the thermal resistance of thepresent example (Sample D) is low, the compressibility is low, thetensile strength and the tearing strength are high, the extensibility islow, and the handling properties during the mounting process are good.Reuse of the formed sheet of thermalconductive silicone gel after thecompression release of the chip and the heat sink was possible.

Example 5

FIGS. 3 A and B are sectional drawings showing a first example of athird formed sheet of thermalconductive silicone gel according to thepresent invention. As is shown in FIGS. 3 A and B, this formed sheet ofthermalconductive silicone gel is composed of a silicone gel layer 1containing a thermalconductive filler, a thin film reinforcement layer 2wherein the silicone gel containing a thermalconductive filler has beenhardened into rubber, and a sheet-shaped reinforcement material 3. FIG.3 A shows an example wherein the sheet-shaped reinforcement material 3is formed in a surface layer on one side of the silicone gel layer 1containing a thermalconductive filler, and a thin film reinforcementlayer 2, wherein the silicone gel containing a thermalconductive fillerhas been hardened into rubber, is formed on this surface layer. FIG. 3 Bshows an example wherein the sheet-shaped reinforcement material 3 isformed in a surface layer on one side of the silicone gel layer 1containing a thermalconductive filler, and a thin film reinforcementlayer 2, wherein the silicone gel containing a thermalconductive fillerhas been hardened into rubber, is formed on both surface layers.

For the silicone gel layer 1 containing a thermalconductive filler andthe thin film reinforcement layer 2, a silicone gel hardened by anaddition reaction, which silicone gel contains the samethermalconductive filler, is used. In addition, at the hardening andformation time, the silicone gel is sandwiched between a PET film towhich about 5 μm of an organohydrogen polysiloxane containing at leasttwo hydrogen atoms bonded to a silicon atom in each molecule have beenapplied, and a PET film to which said organohydrogen polysiloxane hasnot been applied. Alternatively, the silicone gel is sandwiched betweentwo PET films to which said organohydrogen polysiloxane has beenapplied. After the silicone gel is rolled by being passed through a pairof rolls, it is continually passed through a heating furnace. Thus, athin film reinforcement layer hardened into rubber can be formed in asurface layer of one side or both sides of the sheet.

A mesh fabric of polyester fiber, heat-proof nylon fiber, aramid fiber,cotton fiber or the like can be used for the sheet-shaped reinforcementmaterial 3. However, considering the thermal tolerance, polyester fiberor heat-proof nylon fiber are preferable.

The same compositions as listed under Example 1 and Example 3 can beused to produce the silicone gel layer 1 containing a thermalconductivefiller, the thin film reinforcement layer 2 hardened into rubber, andthe sheet-shaped reinforcement material 3.

Using the above compositions, the silicone gel is sandwiched betweenresin films. After the silicone gel is rolled by being passed through apair of rolls, it is passed through a heating furnace with an internalfurnace temperature of 280° C. and a passage velocity through thefurnace of 3 m/min. The characteristics of the formed sheet ofthermalconductive silicone gel obtained under these conditions are shownin Table 9 and 10. The figures shown in these tables refer to a samplehaving a 1.0 mm thick silicone gel layer 1, a 0.03 mm thick thin filmreinforcement layer 2 and a reinforcement material 3 buried to a depthof about 0.2 mm in the silicone gel layer 1, and to a sample with a 2.0mm thick silicone gel layer 1, a 0.05 mm thick thin film reinforcementlayer 2 and a reinforcement material 3 buried to a depth of about 0.3 mmin the silicone gel layer 1.

                  TABLE 9                                                         ______________________________________                                        Typical product properties of Example 5, using Sarcon GR - a A/B              Sample E        Comp. Sample                                                                              Testing Method                                    ______________________________________                                        Thermal 1.5         1.5         Unsteady Hot Wire                             Conductivity                     Method                                       (W/m · K)                                                            Thermal                                                                       Resistance                                                                    (° C./W)                                                               1.0 mm  0.82        0.82        Transistor: TO-3                              2.0 mm  1.52        1.52        Appl. Power: 20 W                                                             for 5 min                                                                     Load: 2 kgf                                   Compression                                                                   Load (kgf)                                                                    Compres-                                                                              1.0 mm  2.0 mm  1.0 mm                                                                              2.0 mm                                                                              Sample Size:                              sion Rate                           25 mm × 25 mm                       10%     23.8    16.2    29.6  22.6   Compression. Vel.:                       20%     57.3    34.2    65.7  48.3   5 mm/min                                 30%     89.3    56.1    107.8 81.1  Load Cell:                                40%     124.7   82.6    154.5 118.1 200 kgf                                   ______________________________________                                         Remarks: Sample E is composed of a formed sheet of thermalconductive          silicone gel with a buried sheetshaped reinforcement material in a surfac     layer of one side of the sheet and a thin film reinforcement layer on the     same side of the sheet. The Comparative Sample is composed of a formed        sheet of thermalconductive silicone gel with a buried sheetshaped             reinforcement material in a center portion of the sheet.                 

                  TABLE 10                                                        ______________________________________                                        Typical material properties of Example 5, using Sarcon GR - a A/B                               Comp.                                                                  Sample E                                                                              Sample  Testing Method                                     ______________________________________                                        Color        gray-black                                                                             gray-black                                                                             --                                             Spec. Gravity                                                                              2.4      2.4      Water Displacement                                                            Method                                         Tens. Strength (kgf/cm.sup.2)                                                              5        5        JIS-K-6301 (No. 2)                             Extensibility (%)                                                                          80       80       JIS-K-6301 (No. 2)                             Tear. Strength (kgf/cm)                                                                    4        4        JIS-K-6301 (Type B)                            Vol. Resistivity (Ω · cm)                                                   1 × 10.sup.18                                                                    1 × 10.sup.13                                                                     JIS-C-2123                                    Isolation Breakdown                                                                        16       16       JIS-C-2123                                     Voltage (kV/mm)                                                               Withstand Voltage                                                                          13       13       JIS-C-2123                                     (kV/mm)                                                                       ______________________________________                                         Remarks: Sample E is composed of a formed sheet of thermalconductive          silicone gel with a buried sheetshaped reinforcement material in a surfac     layer of one side of the sheet and a thin film reinforcement layer on the     same side of the sheet. The Comparative Sample is composed of a formed        sheet of thermalconductive silicone gel with a buried sheetshaped             reinforcement material in a center portion of the sheet.                 

As becomes clear from Tables 9 and 10, the thermal resistance of thepresent example (Sample E) is low, the compressibility is keptcomparatively low, the tensile strength and the tearing strength arehigh, the extensibility is low, and the handling properties during themounting process are good. Reuse of the formed sheet ofthermalconductive silicone gel after the compression release of the chipand the heat sink was possible.

Example 6

Next, a second example of a third formed sheet of thermalconductivesilicone gel according to the present invention is explained. The formedsheet of thermalconductive silicone gel of this example is shown inFIGS. 3 A and B.

In the present example, for the silicone gel layer 1 and the thin filmreinforcement layer 2, a silicone gel containing the samethermalconductive filler is used. In addition, at the hardening andformation time, the silicone gel is covered on one side with a PP filmto which about 5 μm of an organohydrogen polysiloxane containing atleast two hydrogen atoms bonded to a silicon atom in each molecule havebeen applied, and on the other side with a PP film to which saidorganohydrogen polysiloxane has not been applied. Alternatively, thesilicone gel is covered on both sides with PP films to which saidorganohydrogen polysiloxane has been applied. Thus, a thin filmreinforcement layer hardened into rubber can be formed in a surfacelayer of one side or both sides of the sheet.

A mesh fabric of polyester fiber, heat-proof nylon fiber, aramid fiber,cotton fiber or the like can be used for the sheet-shaped reinforcementmaterial 3. However, considering the thermal tolerance, polyester fiberor heat-proof nylon fiber are preferable.

The same compositions as listed under Example 1 and Example 3 can beused to produce the silicone gel layer 1 containing a thermalconductivefiller, the thin film reinforcement layer 2 hardened into rubber, andthe sheet-shaped reinforcement material 3.

Using the above compositions, the silicone gel is formed by the pressforming method. The characteristics of a formed sheet ofthermalconductive silicone gel obtained at 100° C. forming temperature,3 min forming time, and 100 kgf/cm² forming pressure are shown in Table11 and 12. The figures shown in these tables refer to a sample having a1.0 mm thick silicone gel layer 1, a 0.03 mm thick thin filmreinforcement layer 2 and a reinforcement layer 3 with a weight per areaof 55 g/m² (Russell-Net T-280), and to a sample with a 2.0 mm thicksilicone gel layer 1, a 0.05 mm thick thin film reinforcement layer 2and a reinforcement layer 3 with a weight per area of 55 g/m²(Russell-Net T-280) buried to a depth of about 0.3 mm in the siliconegel layer 1.

                  TABLE 11                                                        ______________________________________                                        Typical product properties of Example 6, using Sarcon GR - a A/B              Sample F        Comp. Sample                                                                              Testing Method                                    ______________________________________                                        Thermal 1.5         1.5         Unsteady Hot Wire                             Conductivity                    Method                                        (W/m · K)                                                            Thermal                                                                       Resistance                                                                    (° C./W)                                                               1.0 mm  1.12        1.12        Transistor: TO-3                              2.0 mm  1.71        1.71        Appl. Power: 20 W                                                             for 5 min                                                                     Load: 2 kgf                                   Compression                                                                   Load (kgf)                                                                    Compres-                                                                              1.0 mm  2.0 mm  1.0 mm                                                                              2.0 mm                                                                              Sample Size:                              sion Rate                           25 mm × 25 mm                       10%     25.1    25.4    55.5  39.6  Compression. Vel.:                        20%     65.4    56.8    125.4 69.3  5 mm/min                                  30%     112.2   90.2    176.7 104.4 Load Cell:                                40%     161.0   134.8   >200   154.8                                                                                 200 kgf                                ______________________________________                                         Remarks: Sample F is composed of a formed sheet of thermalconductive          silicone gel with a buried sheetshaped reinforcement material in a surfac     layer of one side of the sheet and a thin film reinforcement layer on the     same side of the sheet. The Comparative Sample is composed of a formed        sheet of thermalconductive silicone gel with a buried sheetshaped             reinforcement material in a center portion of the sheet.                 

                  TABLE 12                                                        ______________________________________                                        Typical material properties of Example 6, using Sarcon GR - a A/B                               Comp.                                                                  Sample F                                                                             Sample   Testing Method                                     ______________________________________                                        Color        gray-black                                                                             gray-black                                                                             --                                             Spec. Gravity                                                                              2.3      2.3      Water Displacement                                                            Method                                         Tens. Strength (kgf/cm.sup.2)                                                              18       18       JIS-K-6301 (No. 2)                             Extensibility (%)                                                                          180      180      JIS-K-6301 (No. 2)                             Tear. Strength (kgf/cm)                                                                    7        7        JIS-K-6301 (Type B)                            Vol. Resistivity (Ω · cm)                                                   1 × 10.sup.13                                                                     1 × 10.sup.13                                                                           JIS-C-2123                             Isolation Breakdown                                                                        18       18       JIS-C-2123                                     Voltage (kV/mm)                                                               Withstand Voltage                                                                          14       14       JIS-C-2123                                     (kV/mm)                                                                       ______________________________________                                         Remarks: Sample F is composed of a formed sheet of thermalconductive          silicone gel with a buried sheetshaped reinforcement material in a surfac     layer of one side of the sheet and a thin film reinforcement layer on the     same side of the sheet. The Comparative Sample is composed of a formed        sheet of thermalconductive silicone gel with a buried sheetshaped             reinforcement material in a center portion of the sheet.                 

As becomes clear from Tables 11 and 12, the thermal resistance of thepresent example (Sample F) is low, the compressibility is keptcomparatively low, the tensile strength and the tearing strength arehigh, the extensibility is low, and the handling properties during themounting process are good. Reuse of the formed sheet ofthermalconductive silicone gel after the compression release of the chipand the heat sink was possible.

As has been explained above, in a formed sheet of thermalconductivesilicone gel according to the present invention, extreme deformation orrupture during the mounting process can be prevented by providing saidsheet with (i) a thin film reinforcement layer hardened into rubber onlyin a surface layer on the upper side, the lower side, or both sides,(ii) a sheet-shaped reinforcement material buried in a surface layer ofthe upper or the lower side, or (iii) a sheet-shaped reinforcementmaterial buried in a surface layer of the upper side or the lower sideof the sheet, and a thin film reinforcement layer hardened into rubberin this surface layer or in a surface layer on both sides of the sheet.

Consequently, the handling characteristics are improved, and thestickiness of the surface with the thin film reinforcement layerhardened into rubber becomes negligible. Furthermore, the orientation ofthe sheet can be chosen at the time of its adhesion. In addition, theformed sheet of thermalconductive silicone gel is not sticky on bothsides. Thus, the sheet cannot easily be stretched apart so that itdeforms extremely or breaks when the contact compression of the chip andthe heat sink is released for maintenance after the mounting. Therefore,the assembly workablility of the chip and the heat sink are improved,because reuse of the sheet becomes possible. Furthermore, when asheet-shaped reinforcement material is buried in a surface layer on oneside of the sheet, the sheet is not easily ruptured during the contactcompression due to extreme unevenness of the contact compression surfaceof the chip or the heat sink. Thus, a stable broad heat transfer surfacecan be ensured, and the reliability of the heat transfer can beimproved. Finally, by ensuring sufficient flexibility in a directionperpendicular to the sheet, it is possible to hold down thecompressibility, and thus deformation or damage due to the contactcompression with electronic parts used in mounting such as chips, heatsinks and boards can be prevented, and the reliability of the electronicpart or unit can be improved.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The embodimentsdisclosed in this application are to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, all changes that come within the meaning and range ofequivalency of the claims are intended to be embraced therein.

What is claimed is:
 1. A formed sheet comprising a sheet-shapedreinforcement material buried on one side of a formed sheet of siliconegel containing a thermoconductive filler.
 2. The formed sheet accordingto claim 1, wherein a silicone gel containing a thermoconductive fillerissandwiched between (a) a resin film onto whose surface a sheet-shapedreinforcement layer has been layered and (b) a resin film onto whosesurface a sheet-shaped reinforcement layer has not been layered, rolledby being continually passed through at least one pair of rolls, andhardened by being continually passed through a heating furnace, wherebya sheet-shaped reinforcement material buried in a surface layer on oneside of the sheet is formed.
 3. The formed sheet according to claim 2,wherein the depth to which the sheet-shaped reinforcement material isburied in a surface layer on one side of the sheet is in the range ofmore than 0 mm but not more than 1 mm.
 4. The formed sheet according toclaim 3, wherein the sheet-shaped reinforcement material buried in asurface layer on one side of the sheet has a mesh fabric structure usingat least one fiber selected from synthetic fiber and natural fiber. 5.The formed sheet according to claim 2, wherein the sheet-shapedreinforcement material buried in a surface layer on one side of thesheet has a mesh fabric structure using at least one fiber selected fromsynthetic fiber and natural fiber.
 6. The formed sheet according toclaim 1, wherein the depth to which the sheet-shaped reinforcementmaterial is buried in a surface layer on one side of the sheet is in therange of more than 0 mm but not more than 1 mm.
 7. The formed sheetaccording to claim 1, wherein the sheet-shaped reinforcement materialburied in a surface layer on one side of the sheet has a mesh fabricstructure using at least one fiber selected from synthetic fiber andnatural fiber.